بسم هللا الرحمن الرحيم

Khartoum University

Faculty of Engineering

Department of Agricultural and Biological engineering

Conceptual Design of Transmission for Small Tractor

This is submitted to Khartoum University in partial fulfillment of the requirement for the degree of B.SC in Agricultural and Biological Engineering

Presented by

Ishag Ahmed Shareef

Omer Mohammed Zain Ahmed Omer

Mustafa Altahir Fadol Murkaz

Nadreen Hassan Ahmed Mohammed

Under supervision:

Dr. Omer Adam Rahama

September 2014

1

Acknowledgment

First of all there is nothing we could’ve done with out the help of Allah.

We want to thank all the people who supported us and helped us with the very best they can do starting

from our parents whom support was very precious and helpful. And our supervisor who believed in us

and helped us to go through the tough times.

And more importantly thanks to our friends from US for their quick response and their helpful

information.

2

Contents 1 Abstract ...... 5 2 CHAPTER ONE ...... 6 2.1 Introduction: ...... 6 3 CHAPTER TWO ...... 8 3.1 PROBLEMS ENCOUNTERED ...... 8 4 CHAPTER THREE ...... 9 4.1 Literature Review ...... 9 4.2 Power transmission system and Outlets:- ...... 12 4.3 Wheels:- ...... 15 4.4 Histories:- ...... 15 1858 – 1919 ...... 15 1930 - 1939 ...... 16 1940- 1949 ...... 16 1950 - 1959 ...... 16 1960 - 1969 ...... 16 1970 - 1979 ...... 16 1980 - 2000 ...... 17 4.5 Traction Analysis Equations:- ...... 17 4.6 Equations for Bevel gear:- ...... 21 4.7 Gear Ratios:- ...... 22 4.8 Equations for Shaft‟s:- ...... 24 4.9 Equations for spring:- ...... 25 5 CHAPTER FOUR ...... 27 5.1 ANALYSIS OF CHASSIS AND DESIGN TRANSMISSION ...... 27 5.2 Chassis Analysis ...... 27 5.3 DESIGN OF SIMPLE TRANSMISSSION ...... 32

3 6 CHAPTER FIVE...... 42 6.1 MATERIAL MECHANICAL DESIGN ...... 42 7 CONCULATION:- ...... 46 8 Recommendations:- ...... 48 9 Appendix ...... 49 10 References ...... 55

4

1 Abstract  To estimate the traction efficiency and actual travel speed from ZOZ chart.  To estimate the drawbar pull and power of drawbar.  The conceptual design simple transmission system for small tractor (gears – shaft – key - bearing - spring). (Sketched in Solid Works).

Hopefully the conceptual of design small tractor would be assisting to design it, develop it and generally makes agricultural an attractive profession.

5

2 CHAPTER ONE

2.1 Introduction: In modern agricultural machines are used to reduce the hour of labor required to produce agricultural product. Machines have been developed that enable agricultural producer to increase the number of acres that they manage or operate.

Agricultural producer use tractor to operate the equipment that is used to till, plant, fertilize, and harvest crop. Modern tractor range in sizes from 10 to 15 horse power (7.5 to 11 kilowatts) to over 400 horse power (over 300 kilowatts). Grain combines with headers up30 feet (9.1 meter) in width are used to harvest grain and seeds crops. Hay other forage crops can be harvested and stored with modern equipment without any manual handling. Cotton, peanuts, fruits, vegetables, and nut crops are harvested almost entirely by specialized harvesting equipment. The development of the machines used in modern agriculture has brought new demand in farmers, ranchers, and other agricultural workers. They must be familiar energy and mechanical forces and have mechanical skills. It is important that they be able to select machines for specific jobs and know how to safely operate, maintain, and repair them. There is a great demand for persons to manufacture, sell, and service the machine used in agricultural production. This is an important part of the power and machinery industry. It includes the equipment and tractor companies, the farm equipment and supply dealers, the independent repair and maintenance shops, the research and development centers, and all other service that are necessary to support production a gricultural‟s needs for machines and equipment.

Our constantly expanding population has required and will continue to demand an ever increasing agricultural production of food and fibers. Some of the increased production that has

6 been realized during the past century must be credited to advances in non-engineering phases in agricultural technology such as better crop varieties, the more effective use of fertilizers and pesticides, and improved cultural practices. A major factor, however, has been the increased utilization of nonhuman energy and of more effective machines and implement. Objectives of the foundation of this project is to design a small tractor helps small farmers owning appointed by the mechanics at work in there a small farm fit, small, and limited income. Our group that will take care of the design and development of agricultural machinery in Sudan beginning of this project, which we ask god that we have the best start for the development of agriculture in Sudan.

We thank the department of agricultural engineering at the University of Khartoum on their best effort in order to promote agricultural and subdivision (agricultural revival) and especially thank Dr. Omer Adam Rahama of the division of design and supervisor of this project and wish them health and wellness.

7

3 CHAPTER TWO

3.1 PROBLEMS ENCOUNTERED

3.1.1.1 Types of problems encountered:

The student approaching the subject of farm machinery engineering might well considered the types of problems most frequently encountered in this field, together with the general methods ordinarily employed in pursuing these problems. Although the variety of the problems that might be encountered is wide, most of them can be grouped into the following general classification.

1- Development of new type of machine. 2- Improvement of a machine, development of a new model similar to existing machines, or design changes to reduce the manufacturing cost of a machine. 3- Comparative testing of several machines or evaluating of the performance of particular machine. 4- Investigation of the effects of a machine or mechanized system upon crop production and/ or economic. 5- Studies relating to the more efficient utilization of existing machines or their adaptability to special situations. 6- Research studies of fundamental problems not specifically related to a particular machine such as the study of the soil dynamics in relation to tillage and traction.

Commercial manufacturing organizations are, of course, concerned primarily with the development and improvement of farm machinery, the ultimate goal being to obtain a product that is useful and acceptable to the farmer and that can be manufactured and sold at a profit. To this end, the farm machinery industry is doing and increasing amount of research, the results of which can be applied to some particular class or group of machines.

8 4 CHAPTER THREE

4.1 Literature Review

4.1.1.1 General:- The agricultural tractor is one of the classes of mobile machines that involves the „traction‟ process. The word 'traction' and name 'tractor' come from the word to „draw‟ or „pull‟ so a tractor is basically a machine for pulling; other mobile machines such as locomotives are in the same class. Vehicles like road trucks and even motor cars, which are essentially vehicles for carrying loads, also involve the traction process.

The tractor is also in the class of machines that involves operation under what are known as 'off- road' conditions. Others in this class include machines used in earth moving, mining and military work, also four-wheel drive motor vehicles for cross - country operation.

4.1.1.2 Justification:- The question is often asked as to what is so special about the tractor and its operation that would justify its study as a machine in its own right. This may be answered by considering the conditions under which the tractor is expected operate 1 - The agricultural soils, on which the tractor operates, are 'weak', they slip (shear) when loaded horizontally and compact (compress) when loaded vertically. 2 - The loading conditions on the tractor are variable from job to job and, for efficient operation, ideally require the tractor to be set up to suit each condition.

3 - The operating conditions for the tractor are highly variable both in time and place, which requires continual monitoring and adjustment of both tractor and implement in operation.

4 - The ground surfaces are rough and sloping, hence both tractor and implement control is difficult; instability is an ever-present danger. This is important because the tractor must be able to be operated by non-specialists

5 - A clearance above growing crops and the ability for the operator to see the ground.

9 4.1.1.3 Development:-

The tractor evolved in the second half of the 19th century and first half of the 20th into its present, conventional, two wheel drive form and four wheel drive variation. This form owes much to history but also the fact that it is an inherently logical arrangement.

 Designers followed early tractor designs that were simply replacements for horses or other draught animals.  The layout takes advantage of the transfer of weight to the main driving wheels at the rear, as the drawbar pull on the tractor increases.  The layout is inherently stable in the horizontal plane because the implement commonly being pulled behind the tractor tends to follow the latter and to pull it into straight line operation.  Rear mounted implements offer a minimum of offset loading and moment in the horizontal plane; this contrasts with, for example side mounted implements.

As a result there has been little or no major change in the basic lay-out of tractor / implement systems over their period of development although there have been major improvements in engines, transmissions, tires, control systems and drivers' accommodation.

4.1.1.4 Classification types:- Tractors may be classified according to their basic form, which in turn depends on the function that each type is designed to achieve. They may be classified as follows: Number of axles  one – walking  two - conventional, riding

Number of driven axles  one - conventional and walking  two - four wheel drive

Ground drive elements  wheels and tires, lugs, strakes  tracks - crawler, track laying

10 Use of wheels  traction – conventional  propulsion / cultivation - power tiller

4.1.1.5 System and Power Outlets:- Tractors are built in many forms and sizes according to the particular functions that they are required to perform. However, in reviewing their performance it is sufficient to consider the major systems and power outlets that are common to most tractors.

The following systems can be identified:-

4.1.1.6 Engine:-

The engine, which is the immediate source of energy for the operation of the tractor, varies in type and size according to the type and size of the tractor to which it is fitted. It is a mechanism which, using air, extracts the energy from the fuel and transforms it into a mechanical (rotational) form.

Its output (in terms of torque, speed and power) is determined by the physical size of the engine (which determines the amount of air that can be drawn in), the fuel burnt in that air and its speed of operation. Many other aspects of engine design and operation affect its performance. These include the engine processes (the cycle of strokes on which it operates), the type of fuel and its method of ignition (spark or compression ignition) and the mechanical details such as the design of the components (pistons, crankshaft, valves) and the services such as the lubrication and cooling systems.

Engines as used in agricultural tractors may be classified as follows:

11 Operational cycle  Two strokes per revolution.  Four strokes per revolution. fuel ignition  Spark - gasoline, petrol, natural gas.  Compression – diesel. air induction  Unlimited- diesel.  Throttled - spark ignition.  Pressurized - super-charged. speed control  Governed – automatic.  Ungoverned – manual.

4.2 Power transmission system and Outlets:-

The transmission systems on the tractor serve to transmit power from the engine to the power outlets are: 1. Traction system (wheels / drawbar / three point linkage). 2. Power Take Off. 3. Hydraulic supply.

The transmission elements which comprise these systems may be classified according to their principle of operation:

Mechanical  Gears.  Belts / chains.

Hydrostatic  Fluid pressure. hydro-kinetic  Fluid momentum - Torque converter.

12 4.2.1.1 1 – Traction transmission:-

4.2.1.1.1 Conventional tractor:

The components generally referred to as the `transmission´ and / or the `gear box´ transmit the rotation of the engine to the rear wheels in the conventional tractor this is usually a mechanical system with shafts, gears etc. The engine rotates at high speed (a few 1000 of rpm) and the tractor wheels must operate at low speed (a few 10 of rpm), the traction transmission has the function of reducing the speed of rotation of the engine to that required for the rear wheels.

The (traction) clutch which is usually of the friction type, is placed between the engine and the transmission It enables the driver to temporarily disconnect the engine from the rest of the transmission and to make a gradual connection when power transmission is required and the tractor begins to move. Usually consist of one or more friction surfaces connected to the engine.

That part of the transmission known as the 'differential' has the function of dividing the drive to the wheels and allowing them to turn at different speeds as the tractor turns a corner. Both wheels still drive because the input torques to them remains equal, but they turn at different speeds, corresponding to the respective radii of the curves on which they are travelling.

Common component in the transmission is the 'final drive' which consists of speed reduction gears after the differential. These are placed in this position near the wheels to avoid the low speed / high torque in the previous parts of the transmission.

4.2.1.1.2 Walking tractor:

The two-wheel or walking tractor the transmission usually consists of a variable speed V belt drive from the engine, which also acts as a clutch as it is tightened or loosened. A

13 small gear-box may then be fitted, which in turn drives the wheels through chains. Such tractors are not usually fitted with a power take-off but while stationary may be used to drive equipment such as a pump. The belt drive to the wheels is removed and is used to drive the attached equipment directly.

4.2.1.2 2 – Power Take of Transmission:-

An ('engine speed') power take-off (PTO) which is frequently fitted to conventional tractors consists of a transmission from the engine to shaft which passes to the outside of the tractor, usually at the rear, and may be engaged to drive attached machines. The power passes from the engine through a friction clutch which is frequently operated with the same pedal as the transmission clutch. This, and an engaging mechanism, allows the drive to the power take-off to be stopped and started as required, independently from the drive to the wheels. Hence the driven machine may continue to operate and process the crop even though the tractor and machine are not moving forward. This is a very convenient arrangement and a great advantage over older tractors with a single clutch and especially over ground driven machines.

A "ground-speed" PTO may also be fitted. Here the drive to the PTO shaft is connected to the drive to the wheels after the traction transmission and hence the PTO speed changes as the traction transmission ratio are changed. The ground speed PTO rotates slowly (a few revolutions per unit distance traveled) and may be used as a replacement for a ground drive on machines such as seed drills where a fixed relationship between the movement of the tractor and the function of the machine is important.

4.2.1.3 3 – Hydraulic supply:-

Here oil under pressure from a hydraulic pump, continuously driven by the engine, is available to operate linear actuators (cylinders, rams) usually for the purpose of controlling (raising and lowering) implements, or driving rotating actuators (motors). One such ram, in-built into the tractor, is used to raise the three-point linkage.

14 4.3 Wheels:- The tractor wheels and associated tyres have the function of supporting the tractor and of converting rotary motion of the engine to linear motion the wheels must be chosen to:

1. Support the weight of the tractor (together with any transferred weight from attached implements) while limiting the sinkage into the soil surface and the resultant rolling resistance. 2. Engage with the soil (or surface) and transmit the traction, braking and steering forces (reactions) while limiting relative movement and the resultant slip / skid / side slip. 3. Provide ground following ability together with some springing and shock absorption.

The important variables in relation to the tires include:-

1. Size (diameter and width) which determines their tractive capacity and rolling resistance. 2. strength, expressed in terms of ply rating, which in turn determines the pressure that can be used and hence the weight that the tire can carry; this in turn also determines the tractive capacity and the rolling resistance.

3. Tread pattern which, together with the surface characteristics, determines the engagement and / or contact with the surface.

4.4 Histories:-

1858 – 1919 . Steam plowing engine by J. W. Fawkes. . Otto patents were issued for an internal combustion engine in 1876. . The first tractor demonstration was held in the United States at Omaha, Nebraska, in 1911. . Smaller, lightweight tractors were introduced.

15 . The frameless-type tractor was introduced. . Cast iron was first used in chassis on the 1917 Fordson tractor . . Oil cooled clutch facings were first used on 1917 Fordson tractor . . The power take-off was introduced on the International 8-16 tractor in 1919. 1920 - 1929 . A highly successful row-crop or all-purpose farm tractor was developed and marketed as the McCormick-Deering Farmall Regular in 1924. . The mechanical rockshaft to lift mounted equipment was introduced in 1927.

1930 - 1939 . Caterpillar introduced the diesel engine in 1931 in one of their crawler tractors. . Rubber tires by Firestone Rubber and Allis-Chalmers were first offered in 1932. . Hydraulic rockshaft replaced the mechanical rockshaft in 1936 on the Deere Model A tractor. . High-compression engines increased and in 1937. . The weight-transfer hitch was introduced in 1938 on the Ford 9N tractor. 1940- 1949 . Remote hydraulic cylinders for mounted and drawn implements were adopted and standardized by SAE and ASAE . Number of lawn and garden tractors expanded rapidly. 1950 - 1959 . Power of tractors increased rapidly. . Percentage of diesel tractors increased. . Refinements such as power steering, automatic transmissions, and transmissions with greater speed selections became widely available.

1960 - 1969 . Much more emphasis was placed on operator comfort and safety. . Full power-shift transmissions became available. . Planetary final drives for the final transmission reduction in large tractors. 1970 - 1979 . Turbocharger and intercoolers were added to diesel engines.

16 . Roll-over protective structures (ROPS) became available. . Most large tractors were equipped with cabs. . Nebraska tractor test included sound level measurements in 1970. 1980 - 2000 . Tractors equipped with electronic sensing and control systems for improved performance. . Introduction of rubber-belted track agricultural vehicles. . Tractor size and power have appeared to reach upper limit of 300 kW.

4.5 Traction Analysis Equations:- The development of empirical traction prediction equations have arrived with the following equations:

4.5.1.1 Motion resistance ratio

………….. (3-1) √

………….. (3-2)

4.5.1.2 Gross traction coefficient

( )( ) ………….. (3-3)

………….. (3-4)

The gross traction coefficient.

Mobility number, decimal.

a gross traction force, N.

Dynamic weight on the wheels, N.

17

4.5.1.3 Mobility number ( )

( ) ( )………….. (3-5)

Cone index.

Section width of wheel, m.

Overall tire diameter, m.

Tire deflection, m.

Tire section height, m.

4.5.1.4 Net traction coefficient

………….. (3-6)

Net traction coefficient, decimal.

The motion resistance ratio, dimensionless.

4.5.1.5 Static Weight Distribution:

………….. (3-7)

………….. (3-8)

W = weight of tractor, N.

= Distance from rear axle centerline to center of gravity, m.

= ground support force on front wheel, N.

18 WB = wheelbase of tractor, m.

4.5.1.6 Dynamic weight distribution:

………….. (3-9)

= dynamic front wheel reactions, N.

Critical drawbar pull, N.

Drawbar height from the horizontal rear wheel centerline, m.

………….. (3-10)

Dynamic rear wheel reactions, N.

Drawbar height from the horizontal front wheel centerline, m.

4.5.1.7 Tires Loading and Unloading:

( ) ………….. (3-11)

Unloaded static rear tire radius, m.

Unloaded static rear tire radius, m.

Rim diameter of rear tire, m.

( ) ………….. (3-12)

Unloaded static front tire radius, m.

Unloaded static front tire radius, m.

Rim diameter of front tire, m.

19 4.5.1.8 Gross traction force:

( )( ) ………….. (3-13)

………….. (3-14)

The gross traction coefficient

a gross traction force, N.

Dynamic weight on the wheels, N.

4.5.1.9 Motion resistance force:

………….. (3-15) √

………….. (3-16)

The motion resistance ratio, dimensionless.

Motion resistance force, N.

4.5.1.10 Net traction force:

………….. (3-17)

Net traction coefficient, decimal.

………….. (3-18)

Net tractive force, N.

Dynamic force, N.

20

4.5.1.11 Traction efficiency:

( )

* + ( ) ………….. (3-19) ( )

Tractive efficiency, decimal.

4.5.1.12 Critical pull:

………….. (3-20)

Critical drawbar pulls in KN.

Drawbar height from the horizontal rear wheel centerline.

4.6 Equations for Bevel gear:-

Pitch Angle: = Σ - ϒ……………. (3-21)

Σ = the shaft angle.

ϒ = angle of the pinion.

Face Angle: o = + δG……….. (3-22)

δG = Dedendum angle of the gear.

Root Angle: = – δG………….. (3-23)

Face Width: F = Ao/3…………. (3-24)

Ao = the outer cone distance.

21

4.7 Gear Ratios:-

= ………….. (3-25)

= ………….. (3-26)

= ………….. (3-27)

Where:

NA= rev per min of small bevel ring.

nA = number of teeth on small bevel ring.

NB = rev per min of medium bevel ring.

nB = number of teeth on medium bevel ring.

Nc = rev per min of large bevel ring.

n c = number of teeth on large bevel ring.

DA= Diameter of small bevel ring.

DB = Diameter of medium bevel ring.

Dc = Diameter of large bevel ring.

22 4.7.1.1 Power, Speed, and Torque:-

Power [kW] = ………….. (3-28)

………….. (3-29)

………….. (3-30)

………….. (3-31)

Where:

TA = torque transmitted by ring A.

TB = torque transmitted by ring B.

TC = torque transmitted ring by A.

TD = torque transmitted by driven bevel D.

Velocity or gear ratio (I g) = number of teeth on driven gear/number of teeth on driver gear.

TD = TA = ………….. (3-32)

23

TD = TB = ………….. (3-33)

TD = TC = ………….. (3-34)

4.8 Equations for Shaft’s:- Shafts subjected to twisting moment or torque only.

………….. (3-35)

Twisting moment in N-m Torsional shear stress,

………….. (3-36)

The power transmitted, watt.

………….. (3-37)

Allowable shear stress, N/ .

Ultimate shear stress for the material MPa. Factor of safety.

Shafts subjected to bending moment only

………….. (3-38)

Bending moment,

Bending stress or allowable tensile stress ,N/ .

………….. (3-39)

Ultimate shear stress, MPa.

Shafts subjected to combined twisting and bending moments

24 The shafts must be designed on the basis of the two moments simultaneously, the following two theories are: - Maximum shear stress theory or Guest‟s theory. It is used for ductile materials such as mild steel.

√( ) ( ) ………….. (3-40)

- Maximum normal shear stress theory or Rankin‟s. it is used for brittle materials such as cast iron.

√( ) ( ) ………….. (3-41)

The maximum normal stress in the shaft, MPa.

4.9 Equations for spring:-

Solid length:

………….. (3-42)

= solid length of spring, in mm. = total number of coils. = diameter of wire, in mm.

Free length:

( ) ………….. (3-43)

= the free length of spring, in mm.

= maximum compression, in Pa or kpa

Spring index:

………….. (3-44)

Spring index. Mean diameter of the coil, mm. Diameter of the wire, mm.

25 Spring rate(or stiffness or spring constant):

………….. (3-45)

Spring rate, Axial load required, N. Deflection of the spring, mm.

Modulus of rigidity for the material of the spring wire, N/

Pitch of coil:

………….. (3-46)

Pitch of the coil,

Stress in helical springs:

( ) ………….. (3-47)

………….. (3-48)

Maximum shear stress in the wire, N/

Shear stress factor. In order to consider the effects of both direct shear as well as curvature of wire:

………….. (3-49)

………….. (3-50)

K = Wahl‟s stress factor.

26 5 CHAPTER FOUR

5.1 ANALYSIS OF CHASSIS AND DESIGN TRANSMISSION

5.1.1.1 Traction system:- Off-road vehicles, such as the agricultural tractor, are often expected to provide a significant amount of tractive capability in excess of that required for self-propulsion on a hard flat surface. In fact, the word “tractor,” derived from the term “traction engine,” indicates the importance placed on developing traction for this type of off- road vehicle. Historically, considerable improvements in traction have been made starting with steel wheels and progressing to steel tracks, bias and then radial-ply pneumatic tires and, more recently, rubber tracks. Of the three principal ways (power take-off, hydraulic outlet, and drawbar) of converting a tractor‟s engine power into useful work, the least efficient but most used method is pulling external loads through the drawbar.

Wismar and Luth (1972) developed traction equations used to define the performance of tires on the soil with both frictional and cohesive properties. The equations have found considerable use by researchers in the tire traction studies.

Brixius (1978) presented new revised Wismar and Luth traction equation s that improved the prediction of tractive performance and extend the range of application. The revised Brixius traction equation have led to a better understanding of the variables involved and provided a technical for recommendations that have been in use in a number of years. Zoz (1987) used the equations to develop a spread procedure that runs an LOTUS 123 for predicting the tractive performance and the required static mass for a given performance of both 2WD and 4WD/MFWD tractors .

5.2 Chassis Analysis The traction prediction equations of Brixius (1987), Wismer and Luth have been used in the Development of the computation various tractor chassis parameters, motion equation to determining maximum drawbar pull based on selected dimensions and weight distributed on the chassis. There are nine steps to identify if that assumption weight acceptable on the

27 front, and rear wheels. Also the traction efficiency is very important to show the ratio between the drawbar power and axle‟s power.

5.2.1.1 1 – Static Weight Distribution:

Firstly identify the center of gravity of the tractor (balance point), and static reaction forces by taken moment at the rear axle using the flowing equation (3-8).

Assumptions:

The total weight of 8131N, and the wheelbase of 1.5m, one over three of the total weight distributed over the front wheel, and two over three of the total weight distributed on the rear wheel(from the OECD), so the static reactions at rear and front wheels were 5424N, 2710N respectively then the center of gravity equal 0.9m.

5.2.1.2 2 – Dynamic weight distribution: Weight transfer refers to the changes in the front and rear wheel reactions that occur when a tractor pulls a drawbar load.

Assumption:

The drawbar pull of 2162 N, and hitch point height of 0.4m.

The calculated dynamic reaction at rear and front wheels axles were 4470 N, and 1756 N, respectively from the equations (3-9), and (3-10).

5.2.1.3 3 – Tires Loading and Unloading: The front and rear tire static unloaded radius and loaded static radius were needed to determine the rolling radius. Front and rear unloaded static radius was determined by the following equations (3-11), and (3-12).

Assumption:

The rear tire section width, and the front tier section width, 0.2 m, and 0.1 m respectively. And the rear and front tires diameters, 0.4 m, and 0.3 m, respectively.

28 The calculated from equation unloaded static rear and front tire radius were 0.4 m, and 0.3 m.

The calculated load static rear and front tire radius were 0.4 m, and 0.3 m, respectively. And the deflection at rear and front tire radius were 0.02 m, and 0.01 m, respectively.

5.2.1.4 4 - Tires and soil parameters: To predict the tractive performance of the tractors we have the flowing original equations developed for bias-ply tire by Brixius (1987). Brixius expressed gross traction ratio, and motion resistance ratio as a function of mobility number and wheel slip. He determined the dimensionless numbers in the flowing equations (3-5).

From the table at soil class (soft and sandy) cone index 480kpa, the tire section height is equal to half the difference between the overall unloaded diameter and rim diameter, then the rear and front mobility number were 13 and 14 from the equation (3-5), respectively.

5.2.1.5 5 - Gross traction force: Knowing all the parameters, calculated the gross traction coefficient of rear and front tires from equation (3-3) were 0.5 and 0.5, respectively. And then calculated gross traction force for rear and front tires from equation (3-4) were 2187 N and 882 N, respectively.

(The slip for soft and sandy soil 14% - 16%) from OECD.

5.2.1.6 6 – Motion resistance force: Knowing all the parameters, calculated the motion resistance ratio for the rear and front tire from equation (3-1) were 0.14 and 0.13, respectively. Then calculated motion resistance force for the rear and front tire from equation (3-2) were 618 N and 233 N, respectively.

5.2.1.7 7 – Net traction force: Calculated the net traction coefficient for both rear and front tires from equation (3-6) were 0.35 and 0.36, respectively. And then calculated the Net tractive force for the rear and front tires also equation (3-6) were 1568 N and 648 N, respectively.

29 5.2.1.8 8 – Traction efficiency: Refers to the fraction of axle power that is converted to drawbar power by the drive wheel. Thus, tractive efficiency is defined in chapter three equations (3-19)

Knowing all the parameters, then calculated the tractive efficiency from ZOZ chart with slip 16% and firm soil drawbar pull to axle‟s pull were 73%.

5.2.1.9 9 - Critical pull: Stability is lost when the weight transfer becomes so large that the front wheels lift off the ground. Blow Equation can be used to calculate the critical drawbar pull at which

stability is lost -- that is, when = 0. Assumption: (The velocity of tractor 6 km\hr).

The drawbar pull will be 10136 N from equation (3-20), from ZOZ chart the drawbar pull to static rear axle‟s force(SRAF) 1.65 then the (SRAF) were 6143N, the drawbar power 14 Kw, and axle‟s power 19N. Also from ZOZ chart the actual velocity almost 12 Km\hr.

The Small Tractor in SolidWorks 2014

30

Rear tire of small tractor in SolidWorks 2014

Front wheel of small tractor in SolidWorks 2014

31 5.3 DESIGN OF SIMPLE TRANSMISSSION

5.3.1.1 Design of bevel gears:

The drive and driven bevel gears in solidwork 2014

From equation (3-21) pitch angles for the three rings (A, , and ) were 65.6 , 53.3 , and 45 respectively. The face width by equation (3-24) for drive gear rings (A, B, and C) were 5mm to all respectively, and for driven gear also 5mm.

Then after revolved the sketch in SolidWorks that the diameter of drive gear rings (A, B, and C) were 100mm, 200mm, and 300mm respectively, and the diameter of driven gear 300mm.

5.3.1.1.1 Gear ratio (single gear train): The gear ratio, or velocity ratio, between the rings and driven bevel gearwheel is in inverse ratio to the number of teeth on each. Equations (3-21), (3-22), and (3-23) to determine the ratios.

32 The diameter of small (A), medium (B), and large(C) drive bevel rings were 100mm, 200mm, and 300mm, respectively. The diameters of driven (D) bevel gear were 300mm.

The numbers of teeth for small (A), medium (B), and large (C) drive bevel rings were 22, 36, and 50, respectively. The numbers of teeth of driven (D) bevel gear were 50.

The ratios of meshed driven bevel gear with small, medium, and large rings were 1:2.2, 1:1.8, and 1:1respectively.

5.3.1.1.2 Shaft design:- The shafts may be designed on the basis of:

1. Strength the following cases may be considered: a) Shafts subjected to twisting moment or torque only from the equations (3-35), (3- 36), and (3-37) b) Shafts subjected to bending moment only from the equations (3-38), and (3-39) c) Shafts subjected to combined twisting and bending moments The shafts must be designed on the basis of the two moments simultaneously, the following two theories are: - Maximum shear stress theory or Guest‟s theory. It is used for ductile materials such as mild steel. From equation (3-40) - Maximum normal shear stress theory or Rankin‟s. It is used for brittle materials such as cast iron. From equation (3-41).

We used AISI 4340 Normalized material to design the shafts, the specifications of this material from SolidWorks (Ultimate shear stress is 80000 N/ ), the bending moment were 150000 N/ , the shaft diameter 50mm for length 500mm.

33

Shaft designed in SolidWorks2014

34 5.3.1.1.3 Key design:- After identify the diameter of shaft form the ASME table we can able to choice the suitable key for the shaft.

Used the rectangular key from the table the dimensions of (width, high, and length) 16mm, 11mm, and 76mm respectively.

Key designed in SolidWorks 2014

5.3.1.1.4 Bearing design:- Also from ASME table for journal bearings after identified type of machinery then I can easy selected suitable bearing for the work.

From the table select from machinery (transmission shafts), from the column of bearing select (light and fixed), then the maximum pressure 0.175 N/ , and all the operating values were 0.025, 7, 0.001, and 2 respectively.

35 5.3.1.1.5 Spring design:- we used spring to help for moving the drive gear away from the drive gear to easy meshing, the type of spring is Helical spring with hard drawn material to identify other parameter like solid length used equation (3-24) is 3mm. Then the free length from the equation (3-43) is 24mm. Spring index 17.7, and module of rigidity 80 kN/ , spring rate from equation (3-45) 0.9 N/ . The maximum shear stress from equation (3-49) is 2763 N/ .

Spring designed in SolidWorks 2014

36 5.3.1.2 Neutral All main shaft bevel rings are positioned so that they do not touch the driven bevel gearwheel. A drive is taken to the lay shaft, but the second shaft will not be turned in neutral position.

5.3.1.3 First gear The first-speed driven bevel gear D on the second shaft is lid outer to engage with ring A on the drive wheel; all other rings are rotate freely in neutral. In this rings, the reduction in speed that occurs as the drive passes through the constant-mesh gears, B and C, is reduced further by the firs-speed gears, D and A.

Ig1 = ( )…………..………… (4-1)

N output 1 = ……….…….. (4-2)

T output 1 = T input x ig1……….. (4-3)

First forward gear (the first power) in SolidWorks 2014

37 5.3.1.4 Second gear The second-speed drive gearwheel D is slid outside to engage with the medium ring B; all the other rings are set rotating freely in the non-driving position.

Ig2 = ( )…………………….. (4-4)

N output 2 = …………..….. (4-5)

T output 2 = T input x ig2……… (4-6)

Second forward gear (the second power) in SolidWorks 2014

38 5.3.1.5 Third gear In this gear position, driven gearwheel D is slid out to mesh with gear C.

Ig3 = ( )…………………… (4-7)

N output 3 = ………………. (4-8)

T output 3 = T input x ig3………….. (4-9)

Third forward gear (the third power) in SolidWorks 2014

39 5.3.1.6 Reverse gear Sliding driven gearwheel on the second shaft to the inner and the same meshed happened but change the direction of rotation of the output shaft.

The simplest rings arrangement uses a multi reverse rings, which is mounted on a face of drive gearwheel.

First reverse gear (the first reverse power)

40

Second reverse gear (the second reverse power)

Third reverse gear (the second reverse power)

41 6 CHAPTER FIVE

6.1 MATERIAL MECHANICAL DESIGN

6.1.1.1 Introduction:- The knowledge of materials and their properties is of great significance for engineer. The machine elements should be made such as materials which has properties Suitable for the conditions of operation. In the addition to this a design engineer must be familiar with the effects which the manufacturing processes and heat treatment have on the properties of the materials in this chapter we shall discuss the commonly used engineering materials in machine design.

One of the most important tasks for a designer is the specification of the material from which any individual component of a product is to be made. The decision must consider a huge number of factors, many of which have been discussed in this chapter. The process of material selection must commence with a clear understanding of the functions and design requirements for the product and the individual component.

The designer should consider the interrelationships among the following:

 The functions of the component.  The component's shape.  The material from which the component is to be made.  The manufacturing process used to produce the component.

6.1.1.2 Classification of engineering materials:- The engineering materials are mainly classification as metals and their alloys such as iron steel, copper, aluminum, etc. None metals such as glass, rubber, plastic.

The metals may be further classified as ferrous metals and non-ferrous metals.

The ferrous metals are those which have the iron as their main constituent, such as cast iron, wrought iron and steel.

42 The non-ferrous metals are those which have a metal other than iron as their main constituent, such as copper, aluminum, brass, tin, zinc, etc.

6.1.1.3 Selection of Materials for Engineering Purposes:- The selection of a proper material, for engineering purposes, is one of the most difficult problems for the designer. The best material is one which serves the desired objective at the minimum cost. The following factors should be considered while selecting the material:

 Availability of the materials.  Suitability of the materials for the working conditions in service.  The cost of the materials.  The important properties, which determine the utility of the material, are physical, chemical and mechanical properties.

We shall now discuss the physical and mechanical properties of the material in the following articles.

6.1.1.4 Mechanical Properties of Metals:- The mechanical properties of the metals are those which are associated with the ability of the material to resist mechanical forces and load. These mechanical properties of the metal include strength, stiffness, elasticity, plasticity, ductility, brittleness, malleability, toughness, resilience, creep and hardness.

 Strength: It is the ability of a material to resist the externally applied forces without breaking or yielding. The internal resistance offered by a part to an externally applied force is called stress.

 Stiffness: It is the ability of a material to resist deformation under stress. The modulus of elasticity is the measure of stiffness.

 Elasticity: It is the property of a material to regain its original shape after deformation when the external forces are removed. This property is desirable for materials used in tools and machines. It may be noted that steel is more elastic than rubber.

43

 Plasticity: It is property of a material which retains the deformation produced under load permanently. This property of the material is necessary for forgings, in stamping images on coins and in ornamental work.  Ductility: It is the property of a material enabling it to be drawn into wire with the application of a tensile force. A ductile material must be both strong and plastic. The ductility is usually measured by the terms, percentage elongation and percentage reduction in area. The ductile material commonly used in engineering practice (in order of diminishing ductility) are mild steel, copper, aluminum, nickel, zinc, tin and lead. The ductility of a material is commonly measured by means of percentage elongation and percentage reduction in area in a tensile test. It is the property of a material opposite to ductility. It is the property of breaking of a material with little permanent distortion. Brittle materials when subjected to tensile loads, snap off without giving any sensible elongation. Cast iron is a brittle material.

 Malleability: It is a special case of ductility which permits materials to be rolled or hammered into thin sheets. A malleable material should be plastic but it is not essential to be so strong. The malleable materials commonly used in engineering practice (in order of diminishing malleability) are lead, soft steel, wrought iron, copper and aluminum.

 Toughness: It is the property of a material to resist fracture due to high impact loads like hammer blows. The toughness of the material decreases when it is heated. It is measured by the amount of energy that a unit volume of the material has absorbed after being stressed up to the point of fracture. This property is desirable in parts subjected to shock and impact loads.

 Machinability: It is the property of a material which refers to a relative case with which a material can be cut. The machinability of a material can be measured in a number of ways such as comparing the tool life for cutting different materials or thrust required to

44 remove the material at some given rate or the energy required to remove a unit volume of the material. It may be noted that brass can be easily machined than steel.

 Resilience: It is the property of a material to absorb energy and to resist shock and impact loads. It is measured by the amount of energy absorbed per unit volume within elastic limit. This property is essential for spring materials.

 Creep: When a part is subjected to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called creep. This property is considered in designing internal combustion engines, boilers and turbines.

 Fatigue: When a material is subjected to repeated stresses, it fails at stresses below the yield point stresses. Such type of failure of a material is known as fatigue. The failure is caused by means of a progressive crack formation which are usually fine and of microscopic size. This property is considered in designing shafts, connecting rods, springs, gears, etc.

 Hardness: It is a very important property of the metals and has a wide variety of meanings. It embraces many different properties such as resistance to wear, scratching, deformation and machinability, etc. It also means the ability of a metal to cut another metal.

45 7 CONCULATION:- All the parameters are done and prepared to actual design.

From ZOZ Chart:

Type of soil slip Traction Drawbar Axle‟s power Actual speed efficiency power Firm sand 16% 73% 14KN 19KN 12Km\hr

Bevel gear design:

Drive gear

Pitch angles Face width Number of Module mm Ring diameter mm teeth mm Ring A 65.6 50 22 6 100 Ring B 53.2º 50 36 6 200 Ring C 45º 50 50 6 300

Driven gear

Pitch angles Face width Number of Module Diameter mm mm teeth mm Driven gear D 45º 50 50 6 300

Shaft design and key:

Material type Ultimate shear stress Bending moment Shaft Shaft length diameter mm mm AISI 4340 80000 15000 50 500 Normalized

46 Material type Key width mm Key high mm Key length mm AISI 4340Normalized 16 11 76

Spring design:

Material No. of Dia. Of Solid Spring Module Maximum Spring Max coil and weir and free index of deflection rate shear pitch mm length rigidity mm stress coil mm mm

Hard 8 and 8 3 24 and 17.7 80 25 0.9 2763 drawn mm 56

47 8 Recommendations:- The design is conceptual to be assembled, designed and tested. It is simple and all necessary precautions were taken in the design of the transmission. However it is recommended that further research be done on it and its performance be evaluated.

48 9 Appendix

Machinery Bearing Maximum Operating values

bearing Absolute

pressure viscosity Z in

(p)in (z)in kg/m-s p in

Auto motile and Main 5.9-12 0.007 2.1 0.8- air-craft engine Crank 10.5-24.5 0.008 1.4 1.8 pin 16-35 0.008 1.12 0.7- Wrist pin 1.4 1.5- 2.2 Four stroke-gas Main 5-8.5 0.02 2.8 0.00 0.6-2 and oil engine Crank 9.8-12.6 0.04 1.4 1 0.6- pin 12.6-15.4 0.065 0.7 1.5 Wrist pin 1.5-2 Two stroke gas Main 3.5-5.6 0.02 3.5 0.00 0.6-2 and oil engine Crank 7-10.5 0.04 1.8 1 0.6- pin 8.4-12.6 0.056 1.4 1.5 Wrist pin 1.5-2 Marine steam Main 3.5 0.03 2.8 0.00 0.7- engines Crank 4.2 0.04 2.1 1 1.5 pin 10.5 0.05 1.4 0.7- Wrist pin 1.2 1.2- 1.7

49 Stationary slow Main 2.8 0.06 2.8 0.00 1-2 speed stream Crank 10.5 0.08 0.84 1 0.9- engine pin 12.6 0.06 0.7 1.3 Wrist pin 1.2- 1.5 Stationary high Main 1.75 0.015 3.5 0.00 1.5-3 speed steam Crank 4.2 0.030 0.84 1 0.9- engine pin 12.6 0.025 0.7 1.5 Wrist pin 1.3- 1.7

Reciprocating Main 1.7 0.03 4.2 0.00 1-2.2 pumps and crank pin 4.2 0.05 2.8 1 0.9- compressors Wrist pin 7.0 0.08 1.4 1.7 1.5-2 Steam Driving 3.85 0.10 4.2 0.00 1.6- locomotive axle 14 0.04 0.7 1 1.8 Crank 28 0.03 0.7 0.7- pin 1.1 Wrist pin 0.8- 1.3 Railway cars Axle 3.5 0.1 7 0.00 1.8-2 1 Steam turbines Main 0.7-2 0.002- 14 0.00 1-2 0.016 1

Generator, Rotor 0.7-1.4 0.025 28 0.00 1-2 motor, 13 centrifugal pumps Transmission Light 0.175 0.025- 7 0.00 2-3

50 shafts ,fixed 1.05 0.060 2.1 1 2.5-4 self- 1.05 2.1 2-3

aligning Heavy

Table 1 Design values for journal bearing

Soil class Cone Index or KPa Typical Operation

Conditions

Soft or sandy soil 350 Rice harvest 480 Disking on plowed ground or low-land logging 700 Spring plowing or earthmoving on moist soil

Medium or tilled soil 850 Planting, field cultivating 1000 Corn harvesting, fall plowing 1200 Wheat harvesting

Firm 1750 Summer plowing, logging in dry season, earthmoving on dry, clay soil.

Table 2 the soft sandy wheel numeric value can obtained from ASAE D49

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Table 3 key sizes related with shaft diameter

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Figure 1 ZOZ chats from OECD

53

Figure 2 Drawbar powers versus drawbar pull for the Farmland tractor at maximum governor setting in various gears. ASAE tests.

Figure 3 Variation of fuel consumption and specific fuel consumption with engine Power for the Farmland tractor engine at maximum governor setting. ASAE tests.

54 10 References 1-Atext book of machine design by R.S.KHURMI AND J.K. GUPTE.

2-Machine Elements in mechanical design Mott.

3-Machaical design by peter Childs.

4-Machanical engineering design 8th edition shingles.

5-The mechanics of tractors –Implement performance .R.H.Macmillan senior Academic Associate.

6- Principles of Farm machinery by R.A.Kepner professor Agricultural engineering University of California Davis California.

7- Agricultural power and Machinery by Jacobs/Harrell

8- www.How staff works .Com

9- www.Wikkipepedia .com

10 - Agricultural Engineering international Development technologies center University of Melbourne

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